Week 10 - Assignment 9 Drag and Lift Force.docx

Week 10 - Assignment 9 Drag and Lift Force.docx - Problem...

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Problem P6.26 F D + F B w = 0 →F D = w F B F D = w F B → F D = w 0 →F D = 175 0 = 175 lb F D = 1 2 ×density of air ×Frontal area×velocity 2 ×C D → F D = 1 2 × ρA v 2 ×C D 175 lb = 1 2 × ( 2.33 × 10 3 slug ft 3 ) × 8 ft 2 × ( 150 mi h × 5280 ft mi × 1 3600 h s ) 2 ×C D 175 slug∙ft s 2 = 451.1 slug∙ft s 2 ×C D →×C D = 0.388 Problem P6.27 ℜ= ρ SAE 30 oil ×υ×d μ SAE 30 oil ℜ= 917 kg m 3 × 2 m s × ( 14 mm× 1 m 1000 mm ) 0.26 kg m∙s = 98 F D = 1 2 × ρ SAE 30 oil × A×υ 2 ×C D →F D = 1 2 × 917 kg m 3 × ( π 4 × ( 14 mm× 1 m 1000 m ) 2 ) × ( 2 m s ) 2 × 1.1 = 0.31 kg∙m s 2 = 0.31 N Problem P6.28 F B F D w = 0 ………. (1) F D = F B w F B = ρ air ×g×V balloon ………. (2)
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V balloon = π D 3 6 →V balloon = π 4 3 6 = 33.51 ft 3 F B = ρ air ×g×V balloon → F B = 2.33 × 10 3 slug / ft 3 × 32.2 ft / s 2 × 33.51 ft 3 = 2.514 lb F D = F B w → F D = 2.514 lb 2.5 lb = 0.014 lb F D = 3 πμDυ→υ = F D 3 μD = 0.014 lb 3 π × 3.8 × 10 7 × 4 = 987 ft / s ℜ= ρ air vD μ air = 2.33 × 10 3 slug / ft 3 × 987 ft / 4 3.8 × 10 7 = 2.4 × 10 7 F D = 1 2 C D ρ air Av 2 →F D = 1 2 C D ρ air
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